The invention relates to temperature-compensated control valves, in particular for hydraulic controls of an automatic transmission for automotive vehicles.
An example of a known temperature compensated control valve is disclosed in German Patent No. 20 17 238. That valve comprises a valve spool that is acted upon by pressure in a valve bore against the force of a valve spring. An additional force from a thermostatic device counteracts the pressure loading and tends to displace the valve spool as temperature increases.
The known temperature-compensated control valve of the German patent is constructed as a regulating valve for establishing a control pressure for operating the control valve circuit of an automatic transmission. It comprises a coil spring arrangement that exerts a valve actuating force on a valve spool by means of a lever arm. That force counteracts the pressure loading. In this way, although the viscosity of the transmission oil varies in accordance with variations in temperature, the valve compensates for the effect of viscosity changes on gear ratio shift timing. The complexity of the structure for effecting that compensation, however, is objectionable.
German Auslegeschrift (Published specification) No. 21 37 160 shows another known hydraulic control that includes an accumulator or pressure reservoir 22 for cushioning the gearshifting clutches and brakes for an automatic transmission. It includes throttling devices 30, 17 and 1 for controlling the outflow from the accumulator under different operating conditions. This design requires suitable control valves or suitable one-way valve combinations, which complicate the design of the hydraulic control.